Ballistic article such as bulletproof vests, helmets, armor plate and other military equipment, structural members of helicopters, aircraft, ships, and vehicle panels and briefcases containing high strength fibers are known. Fibers conventionally used include aramid fibers, fibers such as poly(phenylenediamine terephthalamide), graphite fibers, ceramic fibers, nylon fibers, glass fibers and the like. For these applications, the fibers are ordinarily encapsulated or embedded in a rigid matrix material and, in some instances, are joined with rigid facing layers to form complex composite structures.
U.S. Pat. Nos. 4,403,012: 4,457,985 4,501,856: 4,543,286 4,623,574: 4,650,710 disclose ballistic resistant composite article comprised of networks of high strength fibers in matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resins, and other resins curable below the melting point of the fiber. While such composites provide effective ballistic resistance, A. L. Lastnik, et al. "The Effect of Resin Concentration and Laminating Pressures on Kevlar Fabric Bonded with Modified Phenolic Resin", Technical Report NATICK/TR-84/030, June 8, 1984, have disclosed that an interstitial resin, which encapsulates and bonds the fibers of a fabric, reduces the ballistic resistance of the resultant composite article. Therefore, a need exists to improve the structure of composites to effectively utilize the properties of the high strength fibers.
U.S. Pat. No. 4,623,514, Harpell et al., filed Jan. 14, 1985, and commonly assigned, discloses a simple composites..comprising high strength fibers embedded in an elastomeric matrix. Surprisingly, the simple composite structure exhibits outstanding ballistic protection as compared to simple composite utilizing rigid matrices, the results of which are disclosed therein. Particularly effective are simple composites employing ultra-high molecular weight polyethylene and polypropylene such as disclosed in U.S. Pat. No. 4,413,110.
A limitation of the composites disclosed in the art is that the percentage of resin is at least 10 volume percent. U.S. Pat. No. 4,650,710 discloses that the fiber network comprises at least 50 volume percent of the fabric layer, more preferably at least about 70 volume percent, and most preferably at least about 90 volume percent. This patent notes that the volume percent of elastomer in a fabric layer is preferably less than 15 volume percent, more preferably less than about 10 volume percent, and most preferably less than about 5 volume percent. It is desirable to maintain as high a volume percent of fabric as possible to enhance ballistic resistance.
However, patents such as U.S. Pat. No. 4,623,574 show the difficulty in preparing a composite made of a fabric web within a polymeric matrix. In Table 6, sample 12, when a high amount of fiber was used the sample lacked consolidation and could not be tested.
As armor has progressed so has ballistic technology. Presently, armor is desirable to protect against flechettes. Flechettes are sharpened nail-like projectiles having a sharp end and fins at the end opposite the sharp end. They are essentially metal darts. They are metallic, about 0.15 to 1.5 inches long. It is desirable to develop composites useful as armor which can resist the penetration of sharp projectiles such as flechettes.